TEMPERATURE GUIDED RADIOFREQUENCY CATHETER ABLATION OF MYOCARDIUM - COMPARISON OF CATHETER TIP AND TISSUE TEMPERATURES IN-VITRO

Temperature monitoring during RF ablation has been proposed as a means of controlling the creation of the lesion. However, in vivo studies h ave shown poor correlation between lesion size and catheter Sip temper ature. Thus, we hypothesized a difference between catheter tip and tis sue temperatures during RF catheter ablation, and that this difference may depend on flow passing the ablation site, tip electrode length, a nd catheter-tissue orientation. In vitro studies were performed using four different ablation catheters (tip electrode length: 2, 4, or 6 mm ) with a thermistor or a thermocouple as temperature sensor. Set tempe rature was 70 degrees C and pulse duration was 30 seconds. Pieces of p orcine left ventricle were immersed in a bath of isotonic saline-dextr ose solution at 37 degrees C. The ablation catheters were positioned p erpendicularly, obliquely, or parallel to the endocardium. A temperatu re sensor was inserted from the epicardial side and positioned 1 mm be neath the catheter-tissue interface. Experiments were made with a flow of 200 mL/min passing the ablation site or with no flow. The catheter tip and tissue temperatures differed significantly (P < 0.0001) durin g ablation. This difference increased with time, with flow passing the ablation site, with the length of the tip electrode, and when the cat heter was positioned perpendicularly or obliquely to the endocardium a s compared to the parallel catheter-tissue orientation (P < 0.05). In conclusion, the tissue temperature may far exceed the catheter tip tem perature, and intramyocardial superheating resulting in steam formatio n and popping may occur despite a relatively low catheter tip temperat ure.